1. Field of the Invention
The present invention relates to a technology of creating a scanning plan for an X-ray CT system.
2. Description of the Related Art
An X-ray CT system may irradiate a subject with X-rays from a plurality of directions and process the respective X-rays transmitted through the subject as projection data, thereby reconstructing the inside of the subject as an image. In order to acquire and reconstruct an image of the inside of a subject with this X-ray CT system, there is a need to create a scanning plan beforehand. A scanning plan contains various kinds of setting contents, for example, scanning conditions such as a scanning region irradiated with an X-ray, a tube voltage and tube current of an X-ray tube and a time to irradiate with an X-ray, and scanning methods such as dynamic scanning and helical scanning. The scanning plan data containing such setting contents is outputted to a controller, whereby driving of the X-ray CT system is controlled.
Conventionally, setting of the scanning region and the tube current in the scanning plan is done based on a scout image as shown in, for example, Japanese Unexamined Patent Application Publication No. 2004-298247. A scout image is an X-ray transmission image of a subject to be captured. The X-ray CT system captures scout images from two orthogonal directions, i.e., from the front and side of a subject by dual scanogram imaging beforehand, and causes a display device to display these scout images. An operator inputs the settings of the scanning region and the tube current based on the scout images via a graphical user interface (GUI).
For example, when inputting the scanning region, the operator operates a mouse, a trackball, etc., to draw a desired region as the scanning region on the scout image. A frame body surrounding the region is displayed on the scout image as position mark information that represents the scanning region.
Further, the X-ray CT system acquires the pixel value of the scout image and, from that pixel value, calculates the tube current at a position of the X-ray tube corresponding to a view angle orthogonal to the scout image. View angles other than the view angle orthogonal to the scout image are estimated on the basis of the tube currents obtained based on the scout images from the two orthogonal directions on the assumption that the subject is an ellipse.
Thus, according to the technique of creating a scanning plan with a scout image, the operator needs to estimate the position, range and shape of a subject to be captured such as an organ on the basis of an X-ray transmission image of a single plane or X-ray transmission images of two orthogonal planes, and input a scanning region. It is required that the scanning region accurately includes the subject to be captured in order to obtain a high diagnostic effect, and it is important that the other regions are excluded in order to reduce unnecessary exposure. However, by the conventional method based on the estimation of the operator, it is difficult to precisely set the scanning region.
Further, as described above, in a case where the tube current is calculated at each position on the body axis and at each view angle from an X-ray transmission image of a single plane or X-ray transmission images of two orthogonal planes, the view angles other than the view angle orthogonal to the X-ray transmission image must be approximate values based on values calculated from the X-ray transmission image.